Raman study of the phase transition in RbHSO₄

Abstract

Raman spectra of RbHSO, have been recorded in the temperature range from 6 K to the melting point, 480 K. Analysis of the spectra show that the second order phase transition, at 264 K, is of the order-disorder type. NO soft mode was found. The evolution of the v(0-H) mode frequency with temperature, is consistent with a change of orientation of the hydrogen bonds connecting the disordered SO,-O(H) groups. The spectra are also consistent with the existence of a prototype phase which hs3 been assumed to explain the pseudo-orthorhombic symmetry of the paraelectric and ferroelectric phases.

Neutron and high-pressure X-ray diffraction study of hydrogen-bonded ferroelectric rubidium hydrogen sulfate

“…These results, along with earlier spectroscopic work by Ozaki (1980) and Toupry et al (1981), are consistent with dynamic disorder in the two oxygen positions. Two O atoms of HS(1)O 4 À can be refined against the neutron data obtained in the present study over two split positions each with refined occupancies of 0.51 (2) and 0.49 (2) for O20/21 and 0.50 (2) for O30/31.…”

“…They conclude that one HSO 4 À anion shows disorder in two O-atom positions rather than all four. A Raman spectroscopy study by Toupry et al (1981) found the temperature dependence of the O-H frequency to be consistent with a change in ionic orientation.…”

“…Below T c , interaction between HSO 4 À ions outweighs thermal motion (Toupry et al, 1981). The paraelectric toferroelectric transition therefore involves the ordering of two alternative anionic orientations representing minima between which HS(1)O 4 À ions are able to oscillate in the paraelectric phase.…”

Vibrational spectra and phase transitions in columnar M[M′III(SO4)3] compounds

“…The spectra may be compared with those of H2S04,' KHSO; and RbHS0,. 6 The bridging of the iron atoms by the SO:-ions lengthens the two S-0 distances and shortens the free S=O bonds. In a first approximation the SO, groups can be considered as tetrahedral and in a second approximation of C2, symmetry.…”

Understanding the Mechanism of Ferroelectric Phase Transition in RbHSO4: A High-Pressure Raman Investigation

“…Furthermore, low-temperature Raman spectroscopy studies on the compound revealed the transition to be of the order−disorder type, where the room temperature disordered paraelectric phase is going into an ordered ferroelectric phase after the transition temperature. 12 Gesi and Ozawa have studied the pressure-dependent dielectric constant of RbHSO 4 and found a ferroelectric transition around 0.4 GPa and another transition at 0.75 GPa. 1 They assumed that the crystal structure of RbHSO 4 between 0.4 and 0.75 GPa pressure to be monoclinic with space group Pc, which is the same as the structure at the low-temperature ferroelectric phase.…”